Enhanced ideal strength of thermoelectric half-Heusler TiNiSn by sub-structure engineering

ACS Appl. Mater. Interfaces

et al. 2016

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Abstract:The brittle behavior and low strength of CoSb 3 /TiCoSb interface are serious issues concerning the engineering applications of CoSb 3 based or CoSb 3 /TiCoSb segmented thermoelectric devices. To illustrate the failure mechanism of the CoSb 3 /TiCoSb interface, we apply density functional theory to investigate the interfacial behavior and examine the response during tensile deformations. We find that both CoSb 3 (100)/TiCoSb(111) and CoSb 3 (100)/TiCoSb(110) are energetically favorable interfacial structures. Failure of the CoSb 3 /TiCoSb interface occurs in CoSb 3 since the structural stiffness of CoSb 3 is much weaker than that of TiCoSb. This failure within CoSb 3 can be explained through the softening of the Sb−Sb bond along with the cleavage of the Co−Sb bond in the interface. The failure mechanism the CoSb 3 /TiCoSb interface is similar to that of bulk CoSb 3 , but the ideal tensile strength and failure strain of the CoSb 3 /TiCoSb interface are much lower than those of bulk CoSb 3 . This can be attributed to the weakened stiffness of the Co−Sb framework due to structural rearrangement near the interfacial region.

Section: Structure and Bonding Analysis Of The Cosb 3 /Ticosb Interfacementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Structure and Failure Mechanism of the Thermoelectric CoSb₃/TiCoSb Interface

Hao

ACS Appl. Mater. Interfaces

et al. 2016

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“…Here, we compared the ideal shear strength of Bi 2 Te 3 with various high-performance TE materials [34,[42][43][44][45]. As shown in Fig.…”

Section: -3mentioning

confidence: 99%

Superstrengthening Bi2Te3 through Nanotwinning

Morozov

et al. 2017

Phys. Rev. Lett.

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Bismuth telluride (Bi 2 Te 3 ) based thermoelectric (TE) materials have been commercialized successfully as solid-state power generators, but their low mechanical strength suggests that these materials may not be reliable for long-term use in TE devices. Here we use density functional theory to show that the ideal shear strength of Bi 2 Te 3 can be significantly enhanced up to 215% by imposing nanoscale twins. We reveal that the origin of the low strength in single crystalline Bi 2 Te 3 is the weak van der Waals interaction between the Te1 coupling two Te1─Bi─Te2─Bi─Te1 five-layer quint substructures. However, we demonstrate here a surprising result that forming twin boundaries between the Te1 atoms of adjacent quints greatly strengthens the interaction between them, leading to a tripling of the ideal shear strength in nanotwinned Bi 2 Te 3 (0.6 GPa) compared to that in the single crystalline material (0.19 GPa). This grain boundary engineering strategy opens a new pathway for designing robust Bi 2 Te 3 TE semiconductors for high-performance TE devices. DOI: 10.1103/PhysRevLett.119.085501 The continued use of fossil fuels to satisfy escalating global energy requirements is causing severe unacceptable environmental impact. This has generated renewed interest in thermoelectric (TE) conversion technology to convert waste heat directly into electricity, which involves no CO 2 production, is scalable to large power plants, and involves no moving parts (silent) [1]. Over the past two decades, the conversion efficiency (zT) of TE materials has enhanced remarkably, approaching to ∼1.8 [2-4], putting TE materials on the threshold of commercial applications. However, under severe operation conditions, TE materials suffer from unavoidable thermomechanical stresses from cycling of the temperature gradients, leading to rapid deterioration of material performance and accelerated failure of TE devices [5][6][7]. In order for thermoelectrics to play a significant role in engineering applications to alternative energy, the strength and the toughness must be dramatically enhanced.Industrial low temperature waste heat accounts for almost one-third of total energy consumption [8]. The bismuth telluride (Bi 2 Te 3 ) state-of-the-art TE material has been widely used for TE refrigeration in this temperature range (300-550 K) [9], and is now being considered in the automotive industry for recovering waste heat from exhaust systems. Traditional elemental doping strategies have been successful in significantly improving TE properties [10,11], but they have had little effect on enhancing the mechanical properties [12]. Recently, nano-SiC particles dispersed in Bi 2 Te 3 were reported to enhance mechanical strength compared to pure Bi 2 Te 3 , but with concomitant deterioration of the electronic transport properties [13].A well-known mechanism for strengthening metal alloys is to increase the number of such interfacial boundaries as grain boundaries (GBs) and twin boundaries (TBs). These boundaries can strengthen the material by pinning...

“…To determine the structure − property relation of PbTe, we studied the elastic mechanical properties to provide essential information on the structural stability, as listed in 37,38 This suggests that PbTe has a significantly lower structural stiffness than CoSb 3 and TiNiSn. In addition, we also investigated the elastic mechanical properties of PbSe and PbS, as listed in Table 1.…”

Section: Elastic Properties In Pbtementioning

confidence: 99%

“…The ideal shear strength (3.46 GPa) of PbTe is higher than those of layered TE materials such as Mg 3 Sb 2 (1.95 GPa) and SnSe (0.59 GPa), 40,41 but it is much lower than those of 3D TE materials with 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 12 strong covalent frameworks such as CoSb 3 (7.17 GPa) and TiNiSn (10.52 GPa). 37,38 The PbTe compound shows an extremely high zT value experimentally. 3,4 However, its ideal strength is relatively low.…”

Section: Effect On Ideal Strength Of Pbte By Alloyingmentioning

confidence: 99%

Micro- and Macromechanical Properties of Thermoelectric Lead Chalcogenides

ACS Appl. Mater. Interfaces

Duan

et al. 2017

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Both n-and p-type lead telluride (PbTe) based thermoelectric (TE) materials display high thermoelectric efficiency, but the low fracture strength may limit their commercial applications. In order to find ways to improve these macroscopic mechanical properties we report here the ideal strength and deformation mechanism of PbTe using density functional theory (DFT) calculations. This provides structure-property relationships at the atomic scale that can be applied to estimate macroscopic mechanical properties such as fracture toughness. Among all the shear and tensile paths that examined here, we find the lowest ideal strength of PbTe is 3.46 GPa along the (001)/<100> slip system. This leads to an estimated fracture toughness of 0.28 MPa m 1/2 based on its ideal stress-strain relation, which is in good agreement with our experimental measurement of 0.59 MPa m 1/2 . We find that softening and breaking of the ionic Pb−Te bond leads to the structural collapse. To improve the mechanical strength of PbTe, we suggest strengthening the structural stiffness of the ionic Pb−Te framework through an alloying strategy, such as alloying PbTe with isotypic PbSe or PbS. This point defect strategy has a great potential to develop highperformance PbTe based materials with robust mechanical properties, which may also be applied to other materials and applications.